The present invention relates to an apparatus for the production of upholstery with back-foamed covers, and in particular, for motor car seats.
Various attempts have been made to find a method of placing the piece of cover material into the mold cavity in such a manner that the cover material will be free from folds. If folds are unavoidable, they should be placed reproducibly in prearranged positions and the cover material should sit firmly against the wall of the mold cavity at every point.
It is generally known to use so-called vacuum molds for this purpose. In these molds, the cover material is sucked against the wall of the mold by a vacuum applied through perforations in the wall.
A stretching frame which surrounds the mold cavity is generally also used. The cover material is placed over the lower mold half and is pressed with a controlled pressure against the surface of the lower mold half. Finally, a so-called top ram may be used to push the piece of cover material into the mold cavity. In most cases, all three measures are used together (German Offenlegungsschrift No. 2,746,686). Any one of these measures may, of course, be used alone but the result obtained is less perfect. Even the combination of all three measures has its limits if the piece of upholstery to be produced has a complicated shape (for example with undercut portions) and the mold cavity then, of course, has an equally complicated geometry. At these critical points (e.g. undercut portions) it is extremely difficult to place the cover material firmly against the wall of the mold cavity without excessive direct manual intervention. Even the subsequent process of back-foaming cannot ensure that the cavity of the mold will be completely filled. Imperfectly shaped articles of upholstery are not only unsightly but also unusable and simply constitute waste.
The problem arises of finding a method which ensures that in the manufacture of articles of upholstery of the kind mentioned above which have a complicated shape (which is reflected by a similarly complicated shape of the mold cavity), the cover material will be more completely placed against the wall of the mold cavity at the particularly critical points of the cavity, especially at undercut areas.